start by creating a child theme for the customization.
http://codex.wordpress.org/Child_Themes

http://codex.wordpress.org/Page_Templates

create a custom page template, from a copy of page.php, where you remove the call of the sidebar <?php get_sidebar(); ?>;

call the template file for example fullwidth.php;

this should create the CSS class .page-template-fullwidth-php for the body tag of any page using the template; http://codex.wordpress.org/Function_Reference/body_class

for any help with the formatting, please post a link to your site, to a page using the full width page template.
this you can use in some custom styles to stretch the content area over the full width